The invention relates to eye replacement implants. If an eye has become damaged due to trauma or disease, the damaged eye may have to be eviscerated in which all of the inner contents of the eye are removed, or an enucleation may be performed in which the entire eyeball is removed after severing it from the eye muscles and the optic nerve. Following either of these procedures, it is common practice to fill the resulting void with an orbital implant and subsequently fit an ocular prosthesis that closely resembles the eye. After the implant has been inserted into the eye socket following enucleation or evisceration of the eye, tissues heal over the implant. The ocular prosthesis is then placed over these tissues that have healed over the implant. When properly placed within the orbit, the orbital implant replaces some of the volume lost when the eye was removed and helps to maintain the normal structure of the eyelids and eyebrows. When the ocular prosthesis is properly matched to the other eye and coupled to the implant to move with it, substantially normal appearance of the patient is restored.
Eye replacement devices have been available for a number of years to effect functional and cosmetic improvements for the individual who has suffered the loss of an eye. Early ocular implants used in adults were spheres of glass or other inert solid material which filled the orbit, i.e., eye socket, and were then covered with a prosthesis which approximated the curvature and appearance of the human eye. The problem with these devices is that they were smooth on all sides and therefore could not be attached to the extraocular muscles. As a result, the prosthesis would not move with the functioning eye, and would both disconcert a person looking at the wearer and be a source of embarrassment to the wearer.
Another problem with many implants is migration. Migration is the displacement of the implant relative to its proper position in the patient's ocular socket. At times, the migration of an implant may stretch the covering tissue and cause thinning so that the implant surface may become visible or exposed. Many smooth implants migrate because the tissues and muscles of the patient's eye socket are not attached to the implant to hold the implant in its proper place. Even though the implant is buried beneath tissue and muscles, migration, thinning of tissue over the implant, and extrusion of the implant can still occur. Sometimes the tissues which have previously covered the implant become pressured and necrose, thus allowing bacteria to enter and cause infection. This can occur years after the implant is inserted into a patient.
Many current implant devices are intricate non-spherical designs such as the New-Allen, the Universal, and the Iowa. The Universal implant U.S. Pat. No. 4,731,077 is shown in FIG. 13. The problem with non-spherical implants is that a “stock” prosthesis does not properly fit over their non-spherical shape. Although “custom” fitted (non-stock) prosthesis are readily available in many countries, many other countries do not have access to custom fitted prosthesis, and therefore non-spherical implants such as the Universal do not work properly in many areas of the world.
A number of attempts have been made to overcome these and other problems of implant migration. One common attempt is to make the implant porous. Porous implants contain hundreds and often thousands of pores. The porous surface enables living tissue to grow into the pores and help hold the implant in place. However, the rough surface of these implants often cuts and grinds the covering tissue until the implant is exposed, which can cause infection.
Insertion of porous implants into a patient's orbit is difficult because the rough surface of the implant acts like sand paper to the tissue of the patient's orbit. Many porous implants must be wrapped in a smooth plastic covering as they are being inserted into the patient's orbit so that the porous implant does not cling to tissue of the orbit before it is placed deep in the socket. After the porous implant is in place, the plastic sheet is removed from the surface of the implant. If the porous implant is not placed deep within the socket, proper closure of covering tissue will be forceful and may cause early exposure. Once a rough implant is not deep enough, it can't easily be repositioned deeper into the orbit because it clings to the tissue of the orbit. Further, the surgical removal of a porous implant is very difficult (if ever needed) because tissue grows into the thousands of pores on all sides of the implant. Removal of the implant therefore requires the cutting of much tissue which can be a time consuming and damaging process. Many patients' eye sockets have been destroyed by the removal of a porous implant.
Yet another problem with porous implants is the difficulty of curing infections that occur inside the implant. Oftentimes, tissue will not grow into every one of the thousands of pores in a porous implant. If an infection develops in some of the pores that do not have ingrown tissue, then there is no healthy living tissue in the pores to carry medication to the infected site. If medication cannot reach the infected site, it will be impossible to get rid of the infection, and the implant may have to be removed.
U.S. Pat. No. 4,976,731 (Perry) teaches the use of an orbital implant made of a porous material such as hydroxyapatite. Following implantation of porous implants, the patient's tissue grows into the porous structure of the implant as the scleral sac or other covering is absorbed into the system. The '731 patent teaches that after sufficient healing has occurred, the implant can be drilled to provide a passageway that allows the ocular prosthesis to be attached to the implant by insertion of a peg protruding from and forming a part of the prosthesis. The '731 patent asserts that this will resolve the concern of migration or extrusion of the implant because tissue will also grow into and provide a lining for the drilled passageway. However, the procedure of the '731 patent requires a second surgical procedure which comes with the normal risks of such procedures. In addition, complications have been reported with the use of a peg, including infection of the tissue and granuloma formation around the peg implant.
Therefore, there is a need for an ocular implant that is easy to surgically insert and remove from the patient, is totally covered by the patient's tissues, does not need the addition of a peg, yet still has good motility and does not migrate.